This randomized controlled trial investigated the effects of three different time-restricted eating (TRE) schedules (early, late, and self-selected) combined with usual care (UC) versus UC alone on visceral adipose tissue (VAT) and cardiometabolic health in 197 adults with overweight or obesity over 12 weeks. No significant differences were found in VAT changes between the TRE groups and the UC group (early TRE: -4%, 95% CI -12 to 4, P = 0.87; late TRE: -6%, 95% CI -13 to 2, P = 0.31; self-selected TRE: -3%, 95% CI -11 to 5, P ≥ 0.99). However, the early TRE group showed a more pronounced reduction in subcutaneous adipose tissue (SAT) compared to the UC group (-5%, 95% CI -9 to -1, P = 0.005) and greater reductions in body weight (early TRE: -2.9 kg; late TRE: -2.4 kg; self-selected TRE: -3.1 kg). Early TRE also resulted in decreased fasting glucose and nocturnal mean glucose levels compared to the other groups. Adherence was high (85-88%) across all TRE groups, and no serious adverse events were reported.
The study provides valuable insights into the effects of different TRE schedules on body composition and cardiometabolic health. While it demonstrates that TRE can lead to weight loss and improvements in glucose homeostasis, particularly with early TRE, it also highlights the lack of significant impact on VAT reduction compared to usual care alone. Importantly, the study establishes a clear distinction between correlation and causation regarding TRE's impact on body weight and SAT. The observed changes in these parameters can be attributed to the TRE intervention due to the randomized controlled trial design. However, the lack of significant difference in VAT changes between TRE and UC groups suggests that other factors, such as overall calorie intake or adherence to the Mediterranean diet, may play a more significant role in influencing VAT.
The practical utility of these findings is that TRE, particularly early TRE, can be a useful tool for weight management and improving glucose control. The high adherence rates suggest that it is a feasible approach for individuals with overweight or obesity. However, the lack of significant VAT reduction suggests that TRE may not be the most effective strategy for targeting visceral fat specifically. These findings are consistent with previous research showing mixed results on the effects of TRE on VAT, suggesting that individual responses may vary.
While the study provides valuable guidance for practitioners, uncertainties remain. The optimal duration of TRE for maximizing health benefits is unclear, and the long-term sustainability of TRE needs further investigation. Additionally, the specific mechanisms underlying the observed effects, particularly the reduction in SAT with early TRE, require further exploration. Practitioners should consider individual patient characteristics and preferences when recommending TRE and emphasize the importance of overall dietary quality and adherence.
A critical unanswered question is whether the observed benefits of early TRE on body weight, SAT, and glucose homeostasis are sustained over the long term. Additionally, the lack of significant VAT reduction raises questions about the potential role of other factors, such as energy intake and diet composition. While the methodological limitations, including the relatively short intervention period and partially open-label design, may have affected the study's ability to detect significant differences in VAT, they do not fundamentally undermine the main conclusions regarding the positive effects of TRE on body weight and glucose homeostasis. Future research should focus on longer-term studies with larger sample sizes and fully blinded designs to address these limitations and further elucidate the role of TRE in improving metabolic health.
The study employs a randomized controlled trial design, which is a robust methodology for investigating the effects of interventions.
The study includes a relatively large sample size of 197 participants, increasing the statistical power and generalizability of the findings.
The study investigates an important and clinically relevant topic, the impact of time-restricted eating (TRE) on visceral adipose tissue (VAT) and cardiometabolic health.
The study examines three different TRE schedules, including early, late, and self-selected eating windows, providing a comprehensive comparison.
The study reports high adherence rates across the TRE groups, suggesting that TRE is a feasible dietary approach.
The study did not find significant differences in VAT changes between the TRE groups and the control group. It would be beneficial to explore potential reasons for this lack of difference, such as the role of energy intake or the specific characteristics of the participants.
Implementation: Further analysis could investigate the relationship between energy intake, body weight changes, and VAT reduction in each group. Additionally, exploring potential effect modifiers, such as baseline VAT levels or adherence to the Mediterranean diet, could provide insights into the lack of significant differences.
The study's intervention period was 12 weeks, which may be relatively short to observe significant changes in VAT. Longer-term studies could provide a more comprehensive understanding of the effects of TRE on VAT and cardiometabolic health.
Implementation: Future studies could consider extending the intervention period to 6 months or longer to assess the long-term effects of TRE on VAT and cardiometabolic health.
The study includes a large initial sample size of 2,598 participants, which enhances the statistical power and generalizability of the findings.
The study uses a randomized controlled trial design, which is a robust methodology for investigating the effects of interventions.
The study examines three different TRE schedules (early, late, and self-selected), providing a comprehensive comparison of the effects of different eating window timings.
The study reports detailed baseline characteristics of the participants, allowing for a thorough understanding of the study population.
The study uses objective measures, such as MRI and continuous glucose monitoring, to assess the outcomes, increasing the reliability of the findings.
The study found no significant differences in VAT changes between the TRE groups and the UC group. It would be beneficial to explore potential reasons for this lack of difference, such as the role of energy intake or the specific characteristics of the participants.
Implementation: Further analysis could investigate the relationship between energy intake, body weight changes, and VAT reduction in each group. Additionally, exploring potential effect modifiers, such as baseline VAT levels or adherence to the Mediterranean diet, could provide insights into the lack of significant differences.
The study found that the early TRE group had a more pronounced reduction in subcutaneous adipose tissue (SAT) compared to the UC group. It would be valuable to investigate the potential mechanisms underlying this difference and its clinical implications.
Implementation: Future studies could explore the effects of early TRE on SAT in more detail, including the assessment of SAT distribution and its association with cardiometabolic risk factors. Additionally, investigating the potential role of circadian rhythms and hormonal changes in mediating the effects of early TRE on SAT could provide valuable insights.
The study found that the early TRE group had decreased fasting glucose and nocturnal mean glucose levels compared to the other groups. It would be interesting to explore the potential mechanisms underlying these improvements in glucose homeostasis.
Implementation: Future studies could investigate the effects of early TRE on insulin sensitivity, β-cell function, and other factors involved in glucose metabolism. Additionally, examining the potential role of circadian rhythms and meal timing in mediating the effects of early TRE on glucose homeostasis could provide valuable insights.
Fig. 1 | Study design and participant allocation overview. Study flow diagram. WC, waist circumference; CVD, cardiovascular. Figure created with BioRender.com.
Fig. 2 | Changes in VAT, body weight and composition after intervention. a-e, Changes in VAT volume (a), VAT percentage (b), body weight (c), fat-free mass (d) and fat mass (e) among the UC, early TRE, late TRE and self-selected TRE groups after the 12 week intervention.
Table 2 | Changes in abdominal adipose tissue, body composition, BP, glucose homeostasis, blood lipid profile and dietary intake endpoints in the TRE groups compared with the UC group after the 12 week intervention
Table 3 | Changes in abdominal adipose tissue, body composition, BP, glucose homeostasis, blood lipid profile and dietary intake endpoints in the TRE groups compared with each other after the 12 week intervention
Fig. 3 | 24 h glucose profiles before and after the intervention. a-d, Glucose levels during 24 h as measured by CGM over 14 days in both the baseline and the last 2 weeks of the 12 week intervention for the UC (a), early TRE (b), late TRE (c) and self-selected TRE (d) groups.
The study found that adding time-restricted eating (TRE) to a usual care intervention did not significantly reduce visceral adipose tissue (VAT) compared to usual care alone in adults with overweight or obesity.
The early TRE group showed a more pronounced reduction in subcutaneous adipose tissue (SAT) compared to the usual care group.
Participants in the early, late, and self-selected TRE groups achieved greater reductions in body weight compared to the usual care group.
The early TRE group showed decreased fasting glucose and nocturnal mean glucose levels compared to the other groups.
The study found that TRE was a safe and tolerable dietary approach for obesity management, not associated with any major adverse events.
The study provides a comprehensive comparison of early, late, and self-selected TRE, extending the intervention length to 12 weeks and considering potential sex-related differences.
The study reports high adherence rates across all TRE groups, suggesting that TRE is a feasible dietary approach, even in populations with late dinner times.
The study's sample size and relatively short duration may have limited the ability to detect differences in VAT and other outcomes among the intervention groups.
Implementation: Future studies could consider a larger sample size and a longer intervention period to better assess the effects of TRE on VAT and other cardiometabolic outcomes.
Only personnel responsible for evaluating the primary outcome (VAT), other ectopic fat depots, and fasting blood samples were blinded to the group assignment, while others operated under an open-label approach.
Implementation: Future studies could consider blinding all personnel involved in the study to minimize potential bias.
Including the usual care intervention in the TRE groups could have increased study heterogeneity and decreased statistical power.
Implementation: Future studies could consider comparing TRE to a control group without any intervention or to a control group with a different type of intervention.
Matching fasting duration before testing may have attenuated some of the observed differences in outcomes.
Implementation: Future studies could consider standardizing the fasting duration before testing and ensuring consistent adherence to the fasting protocol.
The absence of follow-up with participants prevents the evaluation of the enduring impacts of TRE over a prolonged timeframe.
Implementation: Future studies could consider including a follow-up period to assess the long-term effects of TRE.
The study was a well-designed randomized controlled trial, which is a robust methodology for investigating the effects of interventions.
The study had a clearly defined protocol with detailed information on the rationale, design, and methods.
The study was registered and approved by regulatory authorities and ethics committees, ensuring ethical conduct.
The study followed the CONSORT reporting guideline for randomized clinical trials, ensuring transparent and complete reporting.
The study had clearly defined eligibility criteria for participants, ensuring a homogenous study population.
The study used a robust randomization method, ensuring balanced allocation of participants to the intervention groups.
The study had a clearly defined primary outcome, visceral adipose tissue (VAT) changes, measured by MRI.
The study included a comprehensive set of secondary outcomes, providing a thorough assessment of the intervention effects.
The study used objective measures, such as MRI and continuous glucose monitoring, to assess the outcomes.
The study had a detailed description of the intervention and control conditions, ensuring replicability.
The study used appropriate statistical methods to analyze the data, including linear mixed-effects models.
The study had a partially open-label design, as personnel in charge of the other measures and the intervention were not blinded to the group assignment.
Implementation: Future studies could consider blinding all personnel involved in the study to minimize potential bias.
The sample size calculation was based on detecting a 10% difference in VAT, but the observed differences were smaller.
Implementation: Future studies may need a larger sample size to detect smaller differences in VAT or other outcomes.
The study did not provide detailed information on the specific content of the educational program for the usual care group.
Implementation: Future studies should provide more details on the educational program, including the topics covered and the materials used.
The study did not assess the participants' chronotype, which may influence the response to time-restricted eating.
Implementation: Future studies could consider assessing chronotype and exploring its potential interaction with the timing of the eating window.